That's no small task for the city with the  highest vehicle density in Europe.

对于欧洲车辆密度最高的城市来说，这是一项不小的任务。

This in turn means it takes longer for a local pileup to move out of a section of the road, increasing vehicle density even more, which eventually adds up to stop-and-go traffic.

这反过来意味着需要更长的时间，才能让局部的一队车辆通过某段道路， 更进一步增加了车流密度，最终导致了停停走走的交通。